In the past, there have been developed different forms or methods to control the discharge of controllable semiconductors, the majority of which are derived from the control forms recommended by manufacturers. These methods utilize voltage and current polarizations applied control gates of the controllable semiconductors at precise moments, in order that said semiconductors convey only that portion of the alternating current semicycles that will be used.
In circuits managing monophasic alternating current the control of which is effected by means of such elements as relaxation oscillators, diacs, neon bulbs, etc., a control range of 0 to 100% is attained. In two or three phased currents which are the most difficult to control with precision, monophasic control systems are applied individually to each phase.
For example, in systems where semiconductors of the above mentioned type are used to open or close circuits of one, two or three phases, a certain degree of control has been attained by means of using high frequency pulse trains or by means of a constant application of signals to their gates. Different specific designs are necessary to control the performance of semiconductors which control power circuits.
In the field of specific application relative to the development of devices to open and close electric circuits, that is, in the field of contactors, a wide variety of contactors have been developed for this sole end, ranging from mechanical to low power solid state contactors, known as solid state relays. Power electronic contactors are also well known, of which some activate their power control components (tiristores) by means of a permanent application of control signals to their gates and other ones activate their control components by means of high frequency pulse trains applied to their gates, thus achieving the conduction of different phases of the current at the moment their polarization is adequate.